//The count-and-say sequence is a sequence of digit strings defined by the recur //sive formula: // // // countAndSay(

//Determine if a 9 x 9 Sudoku board is valid. Only the filled cells need to be v //alidated according to the following r

//Given an array of integers nums sorted in non-decreasing order, find the start //ing and ending position of a given ta

//There is an integer array nums sorted in ascending order (with distinct values //). // // Prior to being passed to yo

//Given two integers dividend and divisor, divide two integers without using mul //tiplication, division, and mod operat

//Implement strStr(). // // Given two strings needle and haystack, return the index of the first occurren //ce of needl

//Given an integer array nums sorted in non-decreasing order, remove the duplica //tes in-place such that each unique el

//You are given an array of k linked-lists lists, each linked-list is sorted in //ascending order. // // Merge all the l

//Given n pairs of parentheses, write a function to generate all combinations of // well-formed parentheses. // // //

//You are given the heads of two sorted linked lists list1 and list2. // // Merge the two lists in a one sorted list. Th

//Given a string s containing just the characters '(', ')', '{', '}', '[' and '] //', determine if the input string is v

//Given the head of a linked list, remove the nth node from the end of the list //and return its head. // // // Examp